1. Field of the Invention
The invention relates to a method of reducing the wettability of the surface of a substrate by providing an adherent layer of fluorosilane on the surface, and to an ink jet recording head including a surface coated with such a layer.
2. Description of Related Technology
The ink jet recording method is a method wherein recording liquid (i.e. ink) is jetted in the form of droplets from an ink ]et recording head toward a receiving surface such as of paper on which the droplets are deposited to effect printing.
In one such method, generally referred to as the continuous method, a stream of electrically charged ink droplets is generated while controlling the charge by a continuous oscillation generating means. The droplets, each with a controlled level of electric charge are jetted toward the receiving surface, e.g. a paper sheet, and the flying course of the droplets is controlled by a pair of deflecting electrodes to which an electric field is applied and between which the droplets pass.
In another such method, generally referred to as the drop-on-demand method, a piezoelectric oscillator is mounted on the ink jet recording head and is mechanically oscillated by application of an electric recording signal.
Typically, the recording head includes a fine pipe for the ink which opens into an orifice. The surface surrounding the orifice may be of the same material as the pipe, or the orifice may be formed in a plate, called the orifice plate, which is attached to the end of the pipe and may be of a material different from that of the pipe. For the purposes of this invention, the orifice plate, if present, is considered to form part of the recording head.
In either case, it has been found desirable for at least a part of the surface of the head to have poor wettability toward the solvent employed for the ink. In some cases, it is also desirable for another part of the surface to have good solvent-wettability. For example, in some head designs, it has been found desirable for at least one part of the surface to remain essentially unwetted by the ink, in order to avoid problems of reliability in operation, and for at least another part to be wettable, e.g. so that another component may be bonded to the face of the head. In one specific embodiment it has been found that where the surface of the area surrounding the orifice is made from certain preferred non-vitreous materials such as metals, ceramics or plastics, problems can arise as a result of the ink wetting the surface and forming a pool which surround the orifice. This pool can interfere with the proper operation of the printer and prevent continuous operation of the printer for more than short periods of time.
There is therefore a need for at least a part of the surface of the recording head, e.g. that part surrounding the orifice, to be treated so that it is less readily wettable by liquids, and in particular by the ink or, more particularly, by the solvent employed in the formulation of the ink, and much research time has been expended on resolving this need. See, for example, in U.S. Pat. Nos. 4,343,013; 4,555,062; and 4,623,906, and European Patent Publications 177,316; 92,229; 92,230; and 121,623.
It is known that the tendency of a surface to be wetted by water or other solvents of the kind used in ink formulations can be reduced by coating the surface with an organic fluoro compound. However, it has been found that prior proposals for applying such fluoro compounds to the surface of non-vitreous substrates such as of metal, ceramics or plastic suffer from one or more disadvantages. For example, PTFE does not have the desired non-wettability for some of the preferred solvents and is difficult to bond to some surfaces. Coatings of fluorinated polymers of the kind proposed for use in mcirocircuitry, on the other hand, do not adhere sufficiently strongly and could be removed during normal procedures used for cleansing the head, such as wiping. Examples of such coatings are SC-721 marketed by 3M Nyebar marketed by Nye, and Galydene marketed by Montedison.
U.S. Pat. No. 4,643,948 proposed coating the surface of an ink jet recording head with a partly fluorinateda alkyl silane and a perfluorinated alkane; however, the only method described for forming the coating involves radio frequency glow discharge.
IBM Technical Disclosure Bulletins Vol. 23, No. 1 of June 1980; Vol. 26, No. 1 of June, 1983; and Vol. 26, No. 3A of Aug. 1983; and U.S. Pat. No. 4,368,476 are representative of proposals for treating the recording head face with a fluorosilicon compound, e.g. by dipping the surface in a dilute solution of the compound. However, it has been found that while some of the coatings could exhibit adequate non-wetting characteristics, their adhesion to non-vitreous surfaces, especially plastic surfaces, is inadequate.
The chosen surface layer, of course, must also be resistant to the ink solvent and this has presented a particular problem in the case of some of the solvents which are now gaining favor, such as those of the glycol or glycol ether kind. For example, it is known, for example from Japanese Kokai 74-31767, to vacuum coat a plastic surface with silicon oxide film and then apply a coating of fluorosilane; however, it has been found that the surface of the coated product thereby obtained is crazed by contact with some of the preferred ink solvents. The layer, e.g. coating, which provides the desired non-wetting characteristics must also adhere well to the substrate, be abrasion resistant, and be resistant to attack by solvents employed in inks used in ink jet printing. Adhesion presents a particular problem where the substrate is non-vitreous and especially where it is formed of plastic.
U.S. Pat. No. 3,953,115 describes forming an adherent optically clear abrasion resistant coating on a plastic opthalmic substrate, using a partially hydrolyzed solution of a vinyl tri(lower alkoxy) silane. U.S. Pat. No. 4,006,271 applies a solution of a hydrolyzed C.sub.1-2 alkyl tri(lower alkoxy) silane to a polycarbonate.